Going Small or Not?

What has really confused me the last couple of games is Nelson kind of switched up the style. Because the Pacers and Bucks were both bigger inside, Nelson tried to match up with their size. He used Foyle in the Pacers game. He started Pietrus, Murphy and Biedrins in the Bucks game.
Why is he switching the style based on the opponent?
They’re clearly better when they play faster, but you need your fastest and most-skilled players on the court. I say play the same against every team. Make big teams run and outrun the small teams. This flopping back and forth doesn’t work. Plus, it takes the players away from their strength. Andris was nearly negated because his strength is not in the halfcourt. Likewise for Pietrus.
If you’re going to play smallball, play smallball.